STRUCTURAL PHLOEM PROTEINS
In vascular plants, long-distance transport of photoassimilates is driven by a pressure gradient within the phloem. It is a highly specialised tissue consisting of a network of living, tube-shaped cells, the sieve elements, connecting all parts of the plant body. An injury of this system can lead to a pressure drop and the loss of sugar, and additionally bears the risk of pathogens to enter the phloem and spread throughout the whole plant.
Structural phloem proteins (P-proteins) assemble to large protein aggregates. Upon wounding, they block the transport in the affected and adjoining sieve elements thereby inhibiting the loss of photoassimilates and preventing phytopathogens from spreading. Two kinds of P-Proteins occur, both encoded by the Sieve Element Occlusion (SEO) gene family:
CONVENTIONAL P-PROTEINS
The conventional P-proteins are parietally arranged at the plasma membrane of the mature sieve elements and were shown to detach and accumulate as a protein plug on the downstream sieve plate upon wounding. Here, the reaction mechanism is of particular interest. Therefore, we use fluorescently labelled P-proteins and other detection systems with confocal laser scanning microscopy on genome edited (CRISPR/Cas9) and transgenic plant lines to observe the reaction in vivo. Furthermore, the physiological role of conventional P-proteins is investigated in model and crop plants by stress experiments and expression analysis via qRT-PCR.
FORISOMES
Forisomes are unique, structural multiprotein complexes exclusively found in the phloem of legumes. When the tissue is injured, they change their shape: The originally long, thin spindle thickens and shortens into a plug. This reaction is induced by calcium ions, is ATP-independent and reversible. In nature, this serves to close wounds within milliseconds and prevents the loss of the nutrient-rich phloem sap. Using modern biotechnological methods, we elucidated the structure and reaction principle of these mechanoproteins. We succeeded in knowledge-based production of large quantities of functional, artificial forisomes and demonstrated their suitability as smart biomaterials. The fusion of forisomes with enzymes, so-called "forizymes", enables the stepwise production and immobilization of single and multi-enzyme complexes, whose special modification allows precise functionalization in microchannels of lab-on-a-chip systems. The combination of their catalytic and stimulus-dependent activity opens up new attractive fields of application in biosensors and microfluidics. We use molecular biology techniques, microscopy and heterologous expression in plants and yeast to unravel the special characteristics of forisomes focusing on the inter- and intramolecular interactions as well as their interaction with calcium.